1. Field of the Invention
The present invention relates to tone transmission in test call generation systems and more particularly to the automatic sending of coded tones in a particular one of several codes in order to transmit the digits comprising a telephone directory number.
2. Description of the Prior Art
In the transmission of telephone directory numbers between switching centers and between a subscriber and a switching center the use of multiple-frequency (MF) signaling and touch calling multiple-frequency signaling (TCMF) respectively, is well known. These signaling schemes employ the use of coded tone signals for the transmission of digits comprising the directory number. A collection of predetermined frequencies forms the basis for each of these signaling codes. Multiplefrequency (MF) signaling selects two out of a group of six frequencies for transmission to form a given digit, whereas touch calling multiple-frequency (TCMF) depends upon the selection of two of eight frequencies for transmission to form a particular digit comprised of a telephone directory number.
Historically, these tone codes have been generated by separate circuits in a telephone office. Heretofore, the technology employed has embodied the use of LC oscillators for the generation of these tones in call initiation systems. Such systems have utilized separate circuits for the generation of these tone frequencies. The use of separate tone generation equipment necessitates the use of separate control logic for the application of these tone signals. Such systems are necessarily complex and require extensive maintenance. In addition, these systems present a multiplicity of design problems and prohibit subsystem modularity.
U.S. Pat. No. 3,719,897 issued on Mar. 6, 1973, to L. A. Tarr, depicts a system in which a tone generator system is used to diagnose tone receiving equipment in a telephone office. In the Tarr patent a single input signal selects a single frequency of either MF or TCMF. Although in the Tarr patent the use of a crystal controlled clock is disclosed, only a single frequency of the two necessary for digit identification is generated.
Therefore, it is an objective of the present invention to provide a single source for the generation of digits comprising a telephone directory number in either the multi-frequency or touch calling multi-frequency codes. Such source provides for simulation of either line or trunk call originations and basic subsystem modularity for simple design.